/*
silverPDF is sponsored by Aleyant Systems (http://www.aleyant.com)

silverPDF is based on PdfSharp (http://www.pdfsharp.net) and iTextSharp (http://itextsharp.sourceforge.net)

Developers: Ai_boy (aka Oleksii Okhrymenko)

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following
conditions:

The above information and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR SPONSORS
BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

*/
#region PDFsharp - A .NET library for processing PDF
//
// Authors:
//   Stefan Lange (mailto:Stefan.Lange@pdfsharp.com)
//
// Copyright (c) 2005-2008 empira Software GmbH, Cologne (Germany)
//
// http://www.pdfsharp.com
// http://sourceforge.net/projects/pdfsharp
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
// DEALINGS IN THE SOFTWARE.
#endregion

using System;
using System.Diagnostics;
using System.Text;
using System.IO;
#if NET_ZIP
using System.IO.Compression;
#else
using PdfSharp.SharpZipLib.Zip.Compression;
using PdfSharp.SharpZipLib.Zip.Compression.Streams;
#endif

namespace PdfSharp.Pdf.Filters
{
  /// <summary>
  /// Implements the FlateDecode filter by wrapping SharpZipLib.
  /// </summary>
  public class FlateDecode : Filter
  {
    /// <summary>
    /// Encodes the specified data.
    /// </summary>
    public override byte[] Encode(byte[] data)
    {
      MemoryStream ms = new MemoryStream();

      // DeflateStream/GZipStream does not work immediately and I have not the leisure to work it out.
      // So I keep on using SharpZipLib even with .NET 2.0.
#if NET_ZIP
      // See http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=97064
      // 
      // Excerpt from the RFC 1950 specs for first byte:
      //
      // CMF (Compression Method and flags)
      //    This byte is divided into a 4-bit compression method and a 4-
      //    bit information field depending on the compression method.
      //
      //      bits 0 to 3  CM     Compression method
      //      bits 4 to 7  CINFO  Compression info
      //
      // CM (Compression method)
      //    This identifies the compression method used in the file. CM = 8
      //    denotes the "deflate" compression method with a window size up
      //    to 32K.  This is the method used by gzip and PNG (see
      //    references [1] and [2] in Chapter 3, below, for the reference
      //    documents).  CM = 15 is reserved.  It might be used in a future
      //    version of this specification to indicate the presence of an
      //    extra field before the compressed data.
      //
      // CINFO (Compression info)
      //    For CM = 8, CINFO is the base-2 logarithm of the LZ77 window
      //    size, minus eight (CINFO=7 indicates a 32K window size). Values
      //    of CINFO above 7 are not allowed in this version of the
      //    specification.  CINFO is not defined in this specification for
      //    CM not equal to 8.
      ms.WriteByte(0x78);

      // Excerpt from the RFC 1950 specs for second byte:
      //
      // FLG (FLaGs)
      //    This flag byte is divided as follows:
      //
      //       bits 0 to 4  FCHECK  (check bits for CMF and FLG)
      //       bit  5       FDICT   (preset dictionary)
      //       bits 6 to 7  FLEVEL  (compression level)
      //
      //    The FCHECK value must be such that CMF and FLG, when viewed as
      //    a 16-bit unsigned integer stored in MSB order (CMF*256 + FLG),
      //    is a multiple of 31.
      //
      // FDICT (Preset dictionary)
      //    If FDICT is set, a DICT dictionary identifier is present
      //    immediately after the FLG byte. The dictionary is a sequence of
      //    bytes which are initially fed to the compressor without
      //    producing any compressed output. DICT is the Adler-32 checksum
      //    of this sequence of bytes (see the definition of ADLER32
      //    below).  The decompressor can use this identifier to determine
      //    which dictionary has been used by the compressor.
      //
      // FLEVEL (Compression level)
      //    These flags are available for use by specific compression
      //    methods.  The "deflate" method (CM = 8) sets these flags as
      //    follows:
      //
      //       0 - compressor used fastest algorithm
      //       1 - compressor used fast algorithm
      //       2 - compressor used default algorithm
      //       3 - compressor used maximum compression, slowest algorithm
      //
      //    The information in FLEVEL is not needed for decompression; it
      //    is there to indicate if recompression might be worthwhile.
      ms.WriteByte(0x49);

      DeflateStream zip = new DeflateStream(ms, CompressionMode.Compress, true);
      zip.Write(data, 0, data.Length);
      zip.Close();
#else
      DeflaterOutputStream zip = new DeflaterOutputStream(ms, new Deflater(Deflater.DEFAULT_COMPRESSION, false));
      zip.Write(data, 0, data.Length);
      zip.Finish();
#endif
      ms.Capacity = (int)ms.Length;
      return ms.GetBuffer();
    }

    /// <summary>
    /// Decodes the specified data.
    /// </summary>
    public override byte[] Decode(byte[] data, FilterParms parms)
    {
      MemoryStream msInput = new MemoryStream(data);
      MemoryStream msOutput = new MemoryStream();
#if NET_ZIP
      // See http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=97064
      // It seems to work when skipping the first two bytes.
      byte header;   // 0x30 0x59
      header = (byte)msInput.ReadByte();
      //Debug.Assert(header == 48);
      header = (byte)msInput.ReadByte();
      //Debug.Assert(header == 89);
      DeflateStream zip = new DeflateStream(msInput, CompressionMode.Decompress, true);
      int cbRead;
      byte[] abResult = new byte[1024];
      do
      {
        cbRead = zip.Read(abResult, 0, abResult.Length);
        if (cbRead > 0)
          msOutput.Write(abResult, 0, cbRead);
      }
      while (cbRead > 0);
      zip.Close();
      msOutput.Flush();
      if (msOutput.Length >= 0)
      {
        msOutput.Capacity = (int)msOutput.Length;
        return msOutput.GetBuffer();
      }
      return null;
#else
      InflaterInputStream iis = new InflaterInputStream(msInput, new Inflater(false));
      int cbRead;
      byte[] abResult = new byte[32768];
      do
      {
        cbRead = iis.Read(abResult, 0, abResult.Length);
        if (cbRead > 0)
          msOutput.Write(abResult, 0, cbRead);
      }
      while (cbRead > 0);
      iis.Close();
      msOutput.Flush();
      if (msOutput.Length >= 0)
      {
        msOutput.Capacity = (int)msOutput.Length;
        return msOutput.GetBuffer();
      }
      return null;
#endif
    }
  }
}
